putting the small screws in for the transistors (4 per board) heat sinks and i was wondering if for some reason (maybe vibration) if the transistor grounds out on the case. what will happen? thinking of buying some plastic screws to hold them down like on the mega squirt has for its transistors.

The shoulder washer are there to insulate the screws from the transistor tab. You need to be careful to align everything and not tighten the nut to much to avoid crushing the shoulder on the washer. If you short the tab to the case, the injector will be stuck open.

Using plastic screws is not a good idea because the transistors get quite hot which means the plastic screws will get loose which means more heat due to less contact with the case. That's a vicious circle that may lead to failure.

My kit only came with 4 mica insulators. I ordered a 5th from digikey for the TIP24C, and found that my voltage was much more stable. I had the board mounted to my MS2 case which is grounded to the MS2.